{
  "subject": "GRB 250311A/MAXI J1457-026: MAXI/GSC detection",
  "eventId": "GRB 250311A",
  "submittedHow": "web",
  "bibcode": "2025GCN.39660....1T",
  "createdOn": 1741664852140,
  "submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
  "circularId": 39660,
  "format": "text/plain",
  "body": "K. Tatano, H. Negoro, M. Nakajima (Nihon U.),  M. Serino, Y. Kawakubo (AGU),\nY. Kudo, H. Shibui, K. Takagi, H. Takahashi, H. Nishio (Nihon U.),\nT. Mihara, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),\nT. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU),\nY. Tsuboi, H. Sugai, N. Nagashima (Chuo U.),\nM. Shidatsu, Y. Niida (Ehime U.),\nI. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech),\nS. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA),\nY. Ueda, Y. Okada, K. Fujiwara (Kyoto U.),\nM. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.),\nK. Yamaoka (Nagoya U.),\nM. Sugizaki (Kanazawa U.),\nW. Iwakiri (Chiba U.),\nT. Kawamuro (Osaka U.)\nreport on behalf of the MAXI team:\n\nThe MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at \n01:55:22 UT on March 11, 2025.\nAssuming that the source flux was constant over the transit,\nwe obtain the source position at\n(R.A., Dec) = (224.318 deg, -2.613 deg) = (14 57 16, -02 36 46) (J2000)\nwith a statistical 90% C.L. elliptical error region\nwith long and short radii of 0.33 deg and 0.28 deg, respectively.\nThe roll angle of long axis from the north direction is 9.0 deg counterclockwise.\nThere is an additional systematic uncertainty of 0.1 deg (90% containment radius).\nThe X-ray flux averaged over the scan was 75 +- 18 mCrab\n(4.0-10.0keV, 1 sigma error).\n\nWithout assumptions on the source constancy, we obtain a rectangular error\nbox for the transient source with the following corners:\n(223.607, -1.537) deg = (14 54 25, -01 32 13) (J2000)\n(223.164, -1.982) deg = (14 52 39, -01 58 55) (J2000)\n(225.099, -3.901) deg = (15 00 23, -03 54 03) (J2000)\n(225.542, -3.455) deg = (15 02 10, -03 27 18) (J2000)\n\nThere was no significant excess flux in the previous transit at 00:22 UT\nand in the next transit at 03:28 UT with an upper limit of 20 mCrab for each.\n\nWe note that the source position is consistent with the position of GRB 250305A \nreported by Fermi-GBM (#39597). We encourage follow-up observations."
}